A device of the known type is known from EP 2 469 264 A1. It comprises a light source and an optical sensor, between which a sample carrier for receiving a fluid to be examined is arranged, said sample carrier being movable relative to the sensor and comprising a window, in which the fluid to be examined is arranged and through which one radiates from a light source, so that particles located in the fluid within the window can be detected by way of the sensor. A multitude of sections of the window and of the fluid located therein can be detected by way of a relative movement between the sample carrier and the optical arrangement, so that the type and the number of the particles located within the window in the fluid can be detected after evaluation in the manner described there. Apart from this mentioned document, WO 2010/063293 A1 as well as WO 2014/094790 A1 are yet also referred to with regard to details of the method.
The sample carrier which is only schematically represented in EP 2 469 264 A1, is integrated into a feed conduit and into a discharge conduit, which each via valves are fixedly connected to the sample carrier and the device and via which a fluid exchange can be effected in the sample carrier, for examining different fluid which is to say liquid samples.
Such an arrangement basically has proven its worth, but however requires a regular maintenance, in particular with the continuous monitoring such as is necessary for example for monitoring drinking water. Thereby, the sample carrier at least in the region of the window is not only to be cleaned from the outside but also from the inside, if for example particles have accumulated there, be this in the form of a film of bacteria, algae growth or likewise. The cleaning of the sample carrier is cumbersome, and moreover the device cannot be used during this time.